Clarify "no events" on timeline

Suggested in #229

core/templates/core/child_detail.html

@@ -44,6 +44,7 @@
                     </a>
                 {% endif %}
             </h3>
+            {% if timeline_objects %}
                 <ul class="timeline m-auto">
                     {% for object in timeline_objects %}
                         <li{% cycle "" ' class="timeline-inverted"' %}>
@@ -66,6 +67,9 @@
                         </li>
                     {% endfor %}
                 </ul>
+            {% else %}
+                <div class="text-center">No events</div>
+            {% endif %}
         </div>
     </div>
 {% endblock %}